Enhanced Osmotic Pressure

Equation 6.12 relates CP to flux (/) and the effective mass-transfer coefficient (kes) for retained solute. For a clean membrane keff = k, which is the boundary layer mass-transfer coefficient from Sherwood correlations [45, 46], However, for a membrane 

The relative contribution to performance loss (TMP rise at constant flux) of resistance PF or CEOP depends on the particle size. For particles 0.5 pm the resistance is relatively small (see effect of particle size in Equation 6.4) and CEOP due to cake height, 8C, is the major effect [48], It is also observed that biofilms can contribute substantial CEOP effects as well as resistance, and in a recent biofouling study more than 50% of the required TMP rise was due to CEOP effects [32]. 

12 Fane, A.G., Wei, X. and Wang, R. (2006) Chapter 7, in Interface Science in Drinking Water Treatment (eds G. Newcombe and 

Principles and Applications of Membrane Bioreactors in Water and Wastewater Treatment, Elsevier, Great Britain. 

Elimelech, M., Gregory, J., Jia, X. and Williams, R.A. (1995) Particle Deposition and Aggregation Measurement, Modelling and Simulation, Butterworth-Heinemann, Woburn, Massachusetts. 

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M. Herzberg, M. Elimelech, Biofouhng of reverse osmosis membranes Role of biofihn-enhanced osmotic pressure. Journal of Membrane Science 2007, 295,11-20. 

In the neighborhood of their c, monodisperse multiarm stars in a good solvent are expected to crystallize. This is a consequence of the concentration-induced enhanced osmotic pressure which outbalances the elastic energy of the sUetched arms. A variety of crystalline phases have been predirted from an effective interactions approach using V r) of eqn [ 18]. At higher concentrations c c, the crystal shoirld melt due to the enhanced osmotic pressure, hence recovering the semidilute polymer solution behavior. However, these prediaions have not been supported convincingly by experimental evidence. It has been... 

Overcoming full-scale plant issues, such as the enhanced osmotic pressure effect due to fouling, which is difficult to capture in the MFI test. 

Due to its browning, fermentability, flavor enhancement, osmotic pressure, sweetness, humectancy (prevention of drying), hygroscopicity (moisture abrsorption), viscosity, and reactivity properties, starch sugar dextrose—is utilized in many food products. The major uses of dextose are the confection, wine, and canning industries. 

Sweetness is primarily a function of the levels of dextrose and maltose present and therefore is related to DE. Other properties that increase with increasing DE value are flavor enhancement, flavor transfer, freezing-point depression, and osmotic pressure. Properties that increase with decreasing DE value are bodying contribution, cohesiveness, foam stabilization, and prevention of sugar crystallization. Com symp functional properties have been described in detail (52). 

Solutions of highly surface-active materials exhibit unusual physical properties. In dilute solution the surfactant acts as a normal solute (and in the case of ionic surfactants, normal electrolyte behaviour is observed). At fairly well defined concentrations, however, abrupt changes in several physical properties, such as osmotic pressure, turbidity, electrical conductance and surface tension, take place (see Figure 4.13). The rate at which osmotic pressure increases with concentration becomes abnormally low and the rate of increase of turbidity with concentration is much enhanced, which suggests that considerable association is taking place. The conductance of ionic surfactant solutions, however, remains relatively high, which shows that ionic dissociation is still in force. 

In RO, a colloidal deposit on the membrane introduces an additional resistance, Rf, and could also cause cake-enhanced concentration osmotic pressure (CEOP) [24]. The CEOP phenomenon is discussed in Section 6.3.4. Large-scale RO plants tend to be operated at a fixed production rate, requiring a fixed average flux. 

The buildup of biofilm on the membrane surface means an additional resistance to solvent flow as well as the possibility of enhancement of CP level by the biofilm, which is similar to the case of colloidal fouling [32,36], In general, the diffusivity is linked to the tortuosity factor of the biofilm [37]. Hence, it is likely that the backdiffusion of solutes in the biofilm on RO is hindered. The enhanced CP is important for two reasons. Firstly, the elevated concentration of solutes at the membrane wall means an increase in the osmotic pressure (CEOP) and hence a loss in the effective TMP. Secondly, the nutrient level is also enhanced and this will further accelerate the growth of the biofilm [32,36]. So, biofouling in RO becomes an interplay between C P and biofilm development. 

Hyaluronan, despite the simplicity of its structure, has a surprisingly wide range of functions. In high concentrations, as found in the ECM of the dermis, it regulates water balance, osmotic pressure, functions as an ion exchange resin, and regulates ion flow. It functions as a sieve, to exclude certain molecules, to enhance the extracellular domain of cell surfaces, particularly the luminal surface of endothelial cells.28 It can also function as a lubricant and as a shock absorber. Hyaluronan can also act as a structural molecule, as in the vitreous of the eye, in joint fluid, and in Wharton s jelly. 

Browning Fermentability Flavor enhancement Flavor transfer Freezing point depression Hygroscopicity Osmotic pressure Sweetness... 

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